toLowerCase()字符串数据时出错，返回undefind

Question

这真的让我很困惑。为什么它不能工作

import express from "express";
import pg from "pg";

const app = express();
const port = 3000;

const db = new pg.Client({
  user: "postgres",
  host: "localhost",
  database: "world",
  password: "Pan970628",
  port: 5432,
});

db.connect();

let quiz = [];

db.query("SELECT * FROM capitals", (err, res) => {
  if (err) {
    console.error("Error executing query", err.stack);
  } else {
    quiz = res.rows;
  }
  db.end();
});

let totalCorrect = 0;

// Middleware
app.use(express.urlencoded({ extended: true }));
app.use(express.static("public"));

let currentQuestion = {};

// GET home page
app.get("/", async (req, res) => {
  totalCorrect = 0;
  await nextQuestion();
  console.log(currentQuestion);
  res.render("index.ejs", { question: currentQuestion });
});

// POST a new post
app.post("/submit", (req, res) => {
  let answer = req.body.answer.trim();
  let isCorrect = false;
  if (currentQuestion.capital.toLowerCase() === answer.toLowerCase()) {
    totalCorrect++;
    console.log(totalCorrect);
    isCorrect = true;
  }

  nextQuestion();
  res.render("index.ejs", {
    question: currentQuestion,
    wasCorrect: isCorrect,
    totalScore: totalCorrect,
  });
});

async function nextQuestion() {
  const randomCountry = quiz[Math.floor(Math.random() * quiz.length)];

  currentQuestion = randomCountry;
}

app.listen(port, () => {
  console.log(`Server is running at http://localhost:${port}`);
});

这是来自控制台的错误消息，只要知道错误是属性未定义即可。

TypeError：无法读取未定义的属性（读取“toLowerCase”） 在文件:///C:/Users/14577/Desktop/Github/Web-Development-Projects/02%20Back-End/8.0%20PostgreSQL/8.2%20World%20Capital%20Quiz/index.js:48:31

我检查了数据库，完全没问题。并且数据类型是字符串。看起来一切都很好，但就是无法工作。它只是告诉我它未定义。

Answer 1

我仔细检查了我运行的代码。看来我只是想念数据库的字段名称。有一点问题